Patent GB-1369108-A (GB)
Title: Electronic ignition spark advance systems
IPC: F02P5/15
Filed: 1972-11-09
Abstract: 1369108 Timing ignition; ignition systems GENERAL MOTORS CORP 9 Nov 1972 [6 Dec 1971] 51672/72 Heading F1B The invention relates to an electronic ignition spark advance system for an internal combustion engine for example for use in a motor vehicle. The system incorporates means 2, 4, 6 for producing a series of crank-shaft position pulses each indicating one degree of rotation of the crank-shaft, means 3, 7, 8 for producing a reference pulse a selected number of degrees of crank-shaft rotation before the top dead-centre position of each piston of the internal-combustion engine and a counter circuit 10 having an input terminal and a plurality of output terminals 10a to 10f each corresponding to a binary code bit for counting the crank-shaft position pulses and producing upon the output terminals thereof the binary code representation of the number of the crank-shaft position pulses counted thereby. An ignition spark advance gate circuit 12 is provided which when enabled gates the series of crankshaft position pulses to the input terminal of the counter circuit 10. The system also incorporates means 20 responsive to the binary code representation, upon the output terminals of the counter circuit, of the number of crank-shaft position pulses counted by the counter circuit equal to the selected number of degrees of crankshaft rotation before the top dead-centre position of each piston of the engine at which each reference pulse is produced for producing an ignition signal, means 14 responsive to each of the reference pulses for producing a start count signal and to each of the ignition signals for producing a full count signal, first delay circuit means 21 responsive to each of the ignition  signals for producing a first engine speed ignition spark advance signal of a pre-selected duration and second delay circuit means 22 responsive to the end of each of the first engine speed ignition spark advance signals for producing a second engine speed ignition spark advance signal of a predetermined duration. The system further incorporates a first count limit circuit means 46 responsive to the binary representation upon the output terminals of the counter circuit of a first selected number of crank-shaft position pulses counted by the counter circuit for producing a first engine speed ignition spark advance limit signal which terminates the first engine speed ignition spark advance signal if the counter circuit counts the first selected number of crank-shaft position pulses prior to the end thereof and a second count limit circuit means 47 responsive to the binary representation upon the output terminals of the counter circuit of a second selected greater number of crank-shaft position pulses counted by the counter circuit for producing a second engine speed ignition spark advance limit signal which terminates the second engine speed ignition spark advance signal if the counter circuit counts the second selected number of crank-shaft position pulses prior to the end thereof. The system still further incorporates circuit means 32 responsive to the end of the second engine speed ignition spark advance signal for producing an engine vacuum ignition spark advance signal, an enabling gate circuit 18 responsive to the start count signals, the first and second engine speed ignition spark advance signals and the engine vacuum ignition spark advance signals for producing an enabling signal for the ignition spark advance gate circuit 12 and to the full count signals for producing a disabling signal for the ignition spark advance gate circuit in the absence of the first and second engine speed and engine vacuum ignition spark advance signals and dwell circuit means 25 responsive to a pre-selected number of the crank-shaft position pulses for initiating the operation of the transistor ignition system to trigger the ignition coil primary winding switching transistor 80 conductive and to each of the ignition signals for initiating the operation of the transistor ignition system to extinguish the ignition coil primary winding switching transistor. If the ignition spark advance is required to begin at a selected engine speed greater than zero, a cut-in circuit may be employed. Such a cut in circuit is described in the Specification. One example of an ignition system suitable for use in conjunction with the electronic ignition spark advance system of the invention is disclosed in United States Specification 3605713.